This proposal entails a comprehensive examination of the mechanisms controlling hepatic ureagenesis and ammonia detoxification in isolated hepatocytes and the isolated perfused liver. The work will address four primary themes: (1) identification of those amino acids serving as precursor to ammonia and urea N in a variety of metabolic conditions; (2) the role of the purine nucleotide cycle in furnishing the nitrogen utilized for the synthesis of either urea of glutamine; (3) the role of various effectors and/or inhibitors of ureagenesis in determining the sources of urea nitrogen; and (4) the effect(s) of hydrogen ion concentration in regulating nitrogen flux through the liver. The latter theme will receive special attention through the study of hepatic N metabolism in rats made acutely or chronically acidotic or alkalotic. A unique feature of the work is the use of physiologic medium containing most of the amino acids normally present in the extracellular fluid, only one of which will be labelled with 15N or 13C. By utilizing both gas chromatography-mass spectrometry and nuclear magnetic resonance to quantify stable isotopic enrichment in ammonia, urea, amino acids and adenine nucleotides, it will be possible to measure metabolite flux and to identify important precursor-product relationships in a manner which has been hitherto impossible. The data do obtained will be of scientific import by deepening our understanding of ureagenesis and of hepatic nitrogen metabolism. The rational clinical management of patients with liver disease presupposes such a scientific foundation.